The field of the present invention is chain adjusting devices for vehicles having a rear fork pivoted to a main vehicle body with an intermediate shaft and a driving shaft coupled together by a chain to drive the vehicle.
Vehicles employing a motorcycle frame and a rear fork pivotally mounted to the frame have incorporated belt transmission mechanisms divided into two portions having an intermediate shaft. The engine output shaft is coupled with the intermediate shaft by means of a chain while the rear drive shaft driving the drive wheel is coupled to the intermediate shaft by a second chain. The intermediate shaft and drive shaft are typically rotatably mounted to the rear fork. Such an arrangement serves to raise the drive train gear ratio and improve chain performance through its positioning and vibration reduction. However, such an arrangement requires adjustment to avoid loosening and slackening of the chains as disclosed in Japanese Patent Application Laid-open No. 60-193789 in which an intermediate shaft is pivoted to an eccentric collar. The eccentric collar is rotatably received in a supporting hole provided in a rear fork to allow the position of the intermediate shaft to be adjusted with rotational adjustment of the collar. To provide support for the intermediate shaft and its bearing, such an eccentric collar conventionally is very large in diameter. In order for the rear fork to support such an eccentric collar, a large supporting hole is required in the fork structure. Such a hole increases the difficulty in creating a strong rear fork. Further, a bending moment is imposed on the intermediate shaft when the chain is under driving tension. Location of the sprocket on the intermediate shaft is influenced by the bending moment to avoid the necessity of excessive supporting structure.